// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_HTTP2_PRIORITY_DEPENDENCIES_H_
#define NET_HTTP2_PRIORITY_DEPENDENCIES_H_

#include <list>
#include <map>

#include "net/spdy/spdy_protocol.h"

namespace net {

// A helper class encapsulating the state and logic to set dependencies of
// HTTP2 streams based on their SpdyPriority and the ordering
// of creation and deletion of the streams.
class NET_EXPORT_PRIVATE Http2PriorityDependencies {
public:
    Http2PriorityDependencies();
    ~Http2PriorityDependencies();

    // Called when a stream SYN is sent to the server.  Note that in the
    // case of server push, a stream may be created without this routine
    // being called.  In such cases, the client ignores the stream's priority
    // (as the server is effectively overriding the client's notions of
    // priority anyway).
    // On return, |*dependent_stream_id| is set to the stream id that
    // this stream should be made dependent on, and |*exclusive| set to
    // whether that dependency should be exclusive.
    void OnStreamSynSent(SpdyStreamId id,
        SpdyPriority priority,
        SpdyStreamId* dependent_stream_id,
        bool* exclusive);

    void OnStreamDestruction(SpdyStreamId id);

private:
    // The requirements for the internal data structure for this class are:
    //     a) Constant time insertion of entries at the end of the list,
    //     b) Fast removal of any entry based on its id.
    //     c) Constant time lookup of the entry at the end of the list.
    // std::list would satisfy (a) & (c), but some form of map is
    // needed for (b).  The priority must be included in the map
    // entries so that deletion can determine which list in id_priority_lists_
    // to erase from.
    using IdList = std::list<std::pair<SpdyStreamId, SpdyPriority>>;
    using EntryMap = std::map<SpdyStreamId, IdList::iterator>;

    IdList id_priority_lists_[kV3LowestPriority + 1];

    // Tracks the location of an id anywhere in the above vector of lists.
    // Iterators to list elements remain valid until those particular elements
    // are erased.
    EntryMap entry_by_stream_id_;
};

} // namespace net

#endif // NET_HTTP2_PRIORITY_DEPENDENCIES_H_
